The NYPD has refused to turn over documents about a 25-year-old homicide conviction handled by discredited ex-Detective Louis Scarcella because doing so would “reveal non-routine criminal-investigation techniques,” a new lawsuit charges.

Ronald Munnerlyn, 53, was convicted of a 1988 murder after he confessed to investigators, including Scarcella, about the fatal Brownsville shooting.

But since then, Scarcella has been dogged by accusations that he coerced witnesses, used the same drug-addled prostitute as a witness in multiple murders and framed innocent men.

Now Munnerlyn’s lawyers, who are fighting to overturn his 1990 conviction for murder and attempted murder in the shooting of two men in Brownsville, say they are being stonewalled by the NYPD, which has shut down Freedom of Information Act requests for police reports and other documents.

Their client’s case is one of about 70 Scarcella cases also under review by the Brooklyn District Attorney’s Office.

“The appeal is further denied because one of the perpetrators has not been apprehended, and disclosure of the requested rec­ords would compromise possible future investigations of this murder case,” a NYPD records officer wrote in denying the FOIA request, the Brooklyn Supreme Court suit states.

Munnerlyn’s lawyers bashed the idea that the rec­ords could endanger any “ongoing” investigation into the 27-year-old case.

“While it is true that another unidentified shooter was allegedly involved in the [Nelson] Rosa and [Marciel] Perez [Jr.] shooting, the NYPD recommended that the case be closed in 1989,” states the suit.

“Releasing the requested documents could not realistically interfere with ‘an ongoing investigation or judicial proceeding.’ In fact, release of these documents may assist in the exoneration of a wrongfully convicted man.”